First I would remove the plywood, then, try raising the front end, make sure the locking nuts are secured after you adjust the legs.
Also try adjusting the legs while the unit is in a high spin with a full load of bath towels, adjust the legs to the point of least vibration.......
but just by you saying that half of your house is shaking should tell you that the vibration is caused more by the foundation than any defect in the washer.
If it is less than a year old, call LG for service. Be advised that they might charge you for the service call if they find that nothing is wrong with your machine.